#include<stdio.h>
#include<stdlib.h>
#include<assert.h>
#include<string.h>
#include<unistd.h>
#include<sys/types.h>
#include<sys/wait.h>
#include<ctype.h>
#include<fcntl.h>


#define LEFT "["
#define RIGHT "]"
#define LABLE "#"
#define DELIM " \t"
#define LINE_SIZE 1024
#define ARGC_SIZE 32
#define EXIT_CODE 44

#define NONE -1
#define IN_RDIR     0
#define OUT_RDIR    1
#define APPEND_RDIR 2


int lastcode = 0;
int quit = 0;
extern char**environ;
char commandline[LINE_SIZE];
char *argv[ARGC_SIZE]; 
char pwd[LINE_SIZE];
char *rdirfilename = NULL;
int rdir = NONE;

//自定义环境变量表
char myenv[LINE_SIZE];
//自定义本地变量表


const char *getusername()
{
   return  getenv("USER");
}

const char *gethostname1()
{
    return getenv("HOSTNAME");
}

void getpwd()
{
    getcwd(pwd,sizeof(pwd));
}

void check_redir(char* cline)
{
    char *pos = cline;
    while(*pos)
    {
        if(*pos == '>')
        {
            if(*(pos+1) == '>')
            {
                *pos++ = '\0';
                *pos++ = '\0';
                
            while(isspace(*pos)) pos++;
            rdirfilename = pos;
            rdir=APPEND_RDIR;
            break;
            }
            else
            {

                *pos = '\0';
                pos++;
            while(isspace(*pos)) pos++;
            rdirfilename = pos;
            rdir=OUT_RDIR;
            break;
            }
        }
        else if(*pos == '<')
        {
            *pos = '\0';
            pos++;
            while(isspace(*pos)) pos++;
            rdirfilename = pos;
            rdir=IN_RDIR;
            break;
        }
        else
        {

        }
        pos++;
    }
}

void interact(char *cline,int size)
{
    getpwd();
    printf(LEFT"%s@%s %s"RIGHT""LABLE" ",getusername(),gethostname1(),pwd);
    char *s= fgets(cline,size,stdin);
    assert(s != NULL);
    (void)s;

    cline[strlen(cline)-1]='\0';

    //ls -a -l > myfile.txt
    check_redir(cline);

}

int splitstring(char cline[],char *_argv[])
{
    int i = 0;
    _argv[i++]=strtok(cline,DELIM);
    while(_argv[i++]=strtok(NULL,DELIM));
    return i-1;
}

void NormalExcute(char*_argv[])
{

        pid_t id=fork();
        if(id < 0)
        {
            perror("fork");
            return;
        }
        else if(id == 0)
        {
            int fd = 0;
            if(rdir == IN_RDIR)
            {
                fd = open(rdirfilename,O_RDONLY);
                dup2(fd,0);
            }
            else if(rdir == OUT_RDIR)
            {

                fd = open(rdirfilename,O_CREAT|O_WRONLY|O_TRUNC,0666);
                dup2(fd,1);
            }
            else if(rdir == APPEND_RDIR )
            {

                fd = open(rdirfilename,O_CREAT|O_WRONLY|O_APPEND,0666);
                dup2(fd,1);
            }

            //让子进程执行命令
            execvp(_argv[0],_argv);
            exit(EXIT_CODE);
        }
        else
        {
            int status=0;
            pid_t rid = waitpid(id,&status,0);
            if(rid == id)
            {
                lastcode = WEXITSTATUS(status);
            }
        }
}

int buildCommand(char *_argv[],int _argc)
{
    if(_argc==2 && strcmp(_argv[0],"cd")==0) 
    {
        chdir(argv[1]);
        getpwd();
        sprintf(getenv("PWD"),"%s",pwd);
        return 1;
    }
    else if(_argc==2 && strcmp(_argv[0],"export")==0)
    {
        strcpy(myenv,_argv[1]);
        putenv(myenv);
        return 1;
    }
    else if(_argc == 2 && strcmp(_argv[0],"echo")==0)
    {
        if(strcmp(_argv[1],"$?") == 0)
        {
            printf("%d\n",lastcode);
            lastcode=0;
        }
        else if(*_argv[1] == '$')
        {
            char *val =getenv(_argv[1]+1);
            if(val) printf("%s\n",val);
        }
        else
        {
            printf("%s\n",_argv[1]);
        }
        return 1;
    }

    //特殊处理一下ls
    if(strcmp(_argv[0],"ls") == 0)
    {
        _argv[_argc++]="--color";
        _argv[_argc] = NULL;
    }

    return 0;
}

int main()
{
    
    while(!quit)
    {
        //1.
        rdirfilename = NULL;
        rdir = NONE;
        //2. 交互问题，获取命令行
        interact(commandline,sizeof(commandline));
        
        //3. 子串分割问题，解析命令行
        int argc=splitstring(commandline, argv);
        if(argc == 0) continue;
        
        //4. 指令的判断
        //debug
        //for(int i=0; argv[i];i++) printf("[%d]: %s\n",i,argv[i]);
        //内建命令，本质上就是一个shell内部的一个函数
        int n=buildCommand(argv,argc);
        
        //5. 普通命令的执行
        if(!n) NormalExcute(argv);
    }

    return 0;
}

